Corrosion inhibitor for stainless steel engine exhaust waterlock

[davidmh]

On my bukh 20 I have a stainless waterlock/silencer fitted, and a want to try to reduce the corrosion over the winter from the mixture of exhaust gas and seawater. It is very difficult to remove the silencer and clean it out, I can run a antifreeze solution into the silencer either on the last run of the ngine or through the outlet pipe of the the waterlock which is accessable. how effective would antifreeze be, is there a better fluid to use? Before you all say " just fit a standard plastic waterlock" I have spent hours measuring up and discussing with the silencer people and no one make a waterlock of the right shape or a shape that will fit the boat. I looked at a bespoke GRP unit and the cost of the special was way above the cost of a stainless special. The engine is 40 year old and still going strong, the owner (me) is nearing 80 and still going strong but in reality when I have to stop sailing the next owner will want to change engine and so the expensive GRP silencer would be a waste. I just want to prolong the current life at least until I have to give up sailing. There are lots of chemists on this forum so I hope you have some ideas for a good inhibiitor.
David MH

 

[vyv_cox]

Automotive antifreeze contains a corrosion inhibitor. I would flush copiously with fresh water drawn from a bucket in the cockpit filled with a hose. After 5 minutes of this turn the hose off, let the bucket run out and tip in 5 litres of ready use antifreeze. Stop the engine just as the antifreeze runs out.

 

[ducked]

Indeed automotive antifreeze (of which there are many flavours) will contain anticorrosion additives, but they probably wont be optimised for your particularly hostile conditions, being designed for the cooling system of IC engines..

Probably you'll get most bang for your buck with extensive hot water (preferably hard but you'll be dependent on what comes out of the tap) rinsing.

Then I believe citric acid passivation is recommended for stainless steel.

 

[davidmh]

Thank for your replies. VYv, I like your method and thanks for the quantity of A/F. I have to do it on my swinging mooring. the way I do the flush is to use the bucket method and top up the bucket during the flush with water from my freshwater tank, which I have to drain down before the boat comes ashore. I do the flush as soon as I come back from a motor down the harbour so the engine is hot and the thermostat open so the solution goes into the block not just along the bypass. I also drain and renew the engine oil at the same time.

Thanks
David MH

 

[ducked]

I've ''flame sprayed' dry exhausts internally with aluminium by putting some beercan and a teaspoon of Portland Cement inside and then running the engine, but that'd be tricky with a wet exhaust, assuming it isnt all steel.